Form submit issues with Squarespace site using Amazon CDN

I have a Squarespace site which I put behind the Amazon Cloudfront CDN for added security. However, the forms on the site don't submit anymore. The submit button simply blinks, and the form does not send. The following console errors are logged:

http://ift.tt/1k4PNRn Failed to load resource: the server responded with a status of 403 (Forbidden) http://ift.tt/1jzi55G Failed to load resource: the server responded with a status of 403 (Forbidden) http://ift.tt/1k4PNRn Failed to load resource: the server responded with a status of 403 (Forbidden)

Any idea what's going on and a work-around? Thanks!